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Fw: {MPML} Forensic Sleuthing Ties Ring Ripples to Impacts From: Ron Baalke

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    A list for asteroid and comet researcher ... From: mpml@yahoogroups.com To: mpml@yahoogroups.com Sent: Friday, April 01, 2011 4:03 AM Subject: {MPML} Digest
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      A list for asteroid and comet researcher

      ----- Original Message -----
      From: mpml@yahoogroups.com
      To: mpml@yahoogroups.com
      Sent: Friday, April 01, 2011 4:03 AM
      Subject: {MPML} Digest Number 3777

      Forensic Sleuthing Ties Ring Ripples to Impacts
      Posted by: "Ron Baalke" baalke@...
      Thu Mar 31, 2011 11:49 am (PDT)


      Forensic Sleuthing Ties Ring Ripples to Impacts
      Jet Propulsion Laboratory
      March 31, 2011

      PASADENA, Calif. - Like forensic scientists examining fingerprints at a
      cosmic crime scene, scientists working with data from NASA's Cassini,
      Galileo and New Horizons missions have traced telltale ripples in the
      rings of Saturn and Jupiter back to collisions with cometary fragments
      dating back more than 10 years ago.

      The ripple-producing culprit, in the case of Jupiter, was comet
      Shoemaker-Levy 9, whose debris cloud hurtled through the thin Jupiter
      ring system during a kamikaze course into the planet in July 1994.
      Scientists attribute Saturn's ripples to a similar object -- likely
      another cloud of comet debris -- plunging through the inner rings in the
      second half of 1983. The findings are detailed in a pair of papers
      published online today in the journal Science.

      "What's cool is we're finding evidence that a planet's rings can be
      affected by specific, traceable events that happened in the last 30
      years, rather than a hundred million years ago," said Matthew Hedman, a
      Cassini imaging team associate, lead author of one of the papers, and a
      research associate at Cornell University, Ithaca, N.Y. "The solar system
      is a much more dynamic place than we gave it credit for."

      From Galileo's visit to Jupiter, scientists have known since the late
      1990s about patchy patterns in the Jovian ring. But the Galileo images
      were a little fuzzy, and scientists didn't understand why such patterns
      would occur. The trail was cold until Cassini entered orbit around
      Saturn in 2004 and started sending back thousands of images. A 2007
      paper by Hedman and colleagues first noted corrugations in Saturn's
      innermost ring, dubbed the D ring.

      A group including Hedman and Mark Showalter, a Cassini co-investigator
      based at the SETI Institute in Mountain View, Calif., then realized that
      the grooves in the D ring appeared to wind together more tightly over
      time. Playing the process backward, Hedman then demonstrated the pattern
      originated when something tilted the D ring off its axis by about 100
      meters (300 feet) in late 1983. The scientists found the influence of
      Saturn's gravity on the tilted area warped the ring into a tightening

      Cassini imaging scientists got another clue when the sun shone directly
      along Saturn's equator and lit the rings edge-on in August 2009. The
      unique lighting conditions highlighted ripples not previously seen in
      another part of the ring system. Whatever happened in 1983 was not a
      small, localized event; it was big. The collision had tilted a region
      more than 19,000 kilometers (12,000 miles) wide, covering part of the D
      ring and the next outermost ring, called the C ring. Unfortunately
      spacecraft were not visiting Saturn at that time, and the planet was on
      the far side of the sun, hidden from telescopes on or orbiting Earth, so
      whatever happened in 1983 passed unnoticed by astronomers.

      Hedman and Showalter, the lead author on the second paper, began to
      wonder whether the long-forgotten pattern in Jupiter's ring system might
      illuminate the mystery. Using Galileo images from 1996 and 2000,
      Showalter confirmed a similar winding spiral pattern. They applied the
      same math they had applied to Saturn - but now with Jupiter's
      gravitational influence factored in. Unwinding the spiral pinpointed the
      date when Jupiter's ring was tilted off its axis: between June and
      September 1994. Shoemaker-Levy plunged into the Jovian atmosphere during
      late July 1994. The estimated size of the nucleus was also consistent
      with the amount of material needed to disturb Jupiter's ring.

      The Galileo images also revealed a second spiral, which was calculated
      to have originated in 1990. Images taken by New Horizons in 2007, when
      the spacecraft flew by Jupiter on its way to Pluto, showed two newer
      ripple patterns, in addition to the fading echo of the Shoemaker-Levy

      "We now know that collisions into the rings are very common - a few
      times per decade for Jupiter and a few times per century for Saturn,"
      Showalter said. "Now scientists know that the rings record these impacts
      like grooves in a vinyl record, and we can play back their history later."

      The ripples also give scientists clues to the size of the clouds of
      cometary debris that hit the rings. In each of these cases, the nuclei
      of the comets - before they likely broke apart - were a few kilometers wide.

      "Finding these fingerprints still in the rings is amazing and helps us
      better understand impact processes in our solar system," said Linda
      Spilker, Cassini project scientist, based at NASA's Jet Propulsion
      Laboratory, Pasadena, Calif. "Cassini's long sojourn around Saturn has
      helped us tease out subtle clues that tell us about the history of our

      The Cassini-Huygens mission is a cooperative project of NASA, the
      European Space Agency and the Italian Space Agency. JPL, a division of
      the California Institute of Technology in Pasadena, manages the
      Cassini-Huygens mission for NASA's Science Mission Directorate,
      Washington. The Cassini orbiter and its two onboard cameras were
      designed, developed and assembled at JPL. The imaging team is based at
      the Space Science Institute in Boulder, Colo. JPL managed the Galileo
      mission for NASA, and designed and built the Galileo orbiter. The New
      Horizons mission is led by Principal Investigator Alan Stern of
      Southwest Research Institute, Boulder, Colo., and managed by the Johns
      Hopkins Applied Physics Laboratory, Laurel, Md., for NASA's Science
      Mission Directorate.

      More information about Cassini can be found at http://www.nasa.gov/cassini .

      Additional contacts: Blaine Friedlander, Cornell University, Ithaca,
      N.Y., 607-254-6235, bpf2@...; Karen Randall, SETI Institute,
      Mountain View, Calif., 650-960-4537, krandall@...; and Joe Mason,
      Space Science Institute, Boulder, Colo., 720-974-5859, jmason@....

      Jia-Rui C. Cook 818-354-0850
      Jet Propulsion Laboratory, Pasadena, Calif.

      Michael Buckley 240-228-7536
      Johns Hopkins University Applied Physics Laboratory, Laurel, Md.


      Spring is Fireball Season
      Posted by: "Ron Baalke" baalke@...
      Thu Mar 31, 2011 11:56 am (PDT)


      Spring is Fireball Season
      NASA Science News
      March 31, 2011

      What are the signs of spring? They are as familiar as
      a blooming Daffodil, a songbird at dawn, a surprising shaft of warmth
      from the afternoon sun.

      And, oh yes, don't forget the meteors.

      "Spring is fireball season," says Bill Cooke of NASA's Meteoroid
      Environment Center. "For reasons we don't fully understand, the rate of
      bright meteors climbs during the weeks around the vernal equinox."

      In other seasons, a person willing to watch the sky from dusk to dawn
      could expect to see around 10 random or "sporadic" fireballs. A fireball
      is a meteor brighter than the planet Venus. Earth is bombarded by them
      as our planet plows through the jetsam and flotsam of space--i.e.,
      fragments of broken asteroids and decaying comets that litter the inner
      solar system.

      In spring, fireballs are more abundant. Their nightly rate mysteriously
      climbs 10% to 30%.

      "We've known about this phenomenon for more than 30 years," says Cooke.
      "It's not only fireballs that are affected. Meteorite falls--space rocks
      that actually hit the ground--are more common in spring as well^1 ."

      Researchers who study Earth's meteoroid environment have never come up
      with a satisfactory explanation for the extra fireballs. In fact, the
      more they think about it, the stranger it gets.

      Consider the following:

      There is a point in the heavens called the "apex of Earth's way." It is,
      simply, the direction our planet is traveling. As Earth circles the sun,
      the apex circles the heavens, completing one trip through the Zodiac
      every year.

      The apex is significant because it is where sporadic meteors are
      supposed to come from. If Earth were a car, the apex would be the front
      windshield. When a car drives down a country road, insects accumulate on
      the glass up front. Ditto for meteoroids swept up by Earth.

      Every autumn, the apex climbs to its highest point in the night sky. At
      that time, sporadic meteors of ordinary brightness are seen in
      abundance, sometimes dozens per night.

      Read that again: Every autumn.

      "Autumn is the season for sporadic meteors," says Cooke. "So why are the
      sporadic fireballs peaking in spring? That is the mystery."

      Meteoroid expert Peter Brown of the University of Western Ontario notes
      that "some researchers think there might be an intrinsic variation in
      the meteoroid population along Earth's orbit, with a peak in big
      fireball-producing debris around spring and early summer. We probably
      won't know the answer until we learn more about their orbits^2 ."

      To solve this and other puzzles, Cooke is setting up a network of smart
      meteor cameras around the country to photograph fireballs and
      triangulate their orbits. As explained in the Science@NASA story What's
      Hitting Earth?
      he's looking for places to put his cameras; educators are encouraged to
      get involved. Networked observations of spring fireballs could
      ultimately reveal their origin.

      "It might take a few years to collect enough data," he cautions.

      Until then, it's a beautiful mystery. Go out and enjoy the night sky. It
      /is/ spring, after all.

      Author: Dr. Tony Phillips
      Credit: Science@NASA
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